1. Field of the Invention
This invention relates to electromagnetic radiation detection devices. More particularly, this invention relates to electromagnetic radiation detection devices which may be worn by an individual to alert such an individual of harmful levels of electromagnetic energy over a broadband of frequencies.
2. Description of Prior Art
The use of high power radio and microwave frequencies in the military, commercial and consumer applications has grown substantially. The applications of high power electromagnetic sources are numerous, including for example, radar, satellite communication ground terminals, radio transmitting antennas and microwave ovens.
One problem with high power electromagnetic radiation is its potential harmful effects on lining tissue. The American National Standards Institute have established safety guidelines to prevent exposure to harmful levels of electromagnetic radiation.
Harmful levels of electromagnetic radiation may not be detected by an individual until permanent damage results. Accordingly, a work place in the vicinity of high power electromagnetic sources can be a dangerous environment. Therefore, there is a need for a device which can sense and measure electromagnetic radiation and provide an alert signal indicating harmful ambient levels. Furthermore, because of the numerous applications of electromagnetic sources and the multitude of frequencies generated, such electromagnetic radiation detection devices having a broadband frequency performance are desirable.
Broadband electromagnetic radiation detection devices have been used in the art for many years. For example, U.S. Pat. No. 3,931,573 assigned to the assignee of the present invention, discloses a hand-held radiation detector. However, hand-held radiation detectors may sometimes be cumbersome and inconvenient. Therefore, radiation hazard meters which can be worn by an individual are both practical and desirable.
When constructing a personal radiation hazard meter, electromagnetic interference from a human body is a concern. It is known that interference in the form of electromagnetic scattering results when electromagnetic radiation reflects off the human body. Such scattered reflections interfere with the electromagnetic radiation being detected by the radiation detector and introduce inaccuracies.
To minimize body interference, the radiation sensors of personal radiation hazard meters require shielding of the electromagnetic radiation sensor from the user's body. The shield, however, may produce its own source of interference due to unwanted reflections.
The use of lossy material as a radiation absorber to absorb reflective radiation is well known in the art. However, lossy material has an acceptable reflective characteristic over a limited frequency range. Generally, the more highly absorbent the lossy material is the smaller the useful frequency range it has. The relatively large operational bandwidth of the monitor precludes the use of a single type of lossy material. This property of lossy material suggests that the use of multiple layers of lossy material having different absorption (and, accordingly, reflective) characteristics would be most effective in eliminating reflective interference from the conductive shield.
An example of this technique is shown in U.S. Pat. No. 5,168,265 (Aslan). A less absorbent/reflective lossy material is disposed behind the radiation sensor, then at least a second layer of more absorbent/reflective lossy material is disposed behind the first layer and in front of the shield. The lamination of lossy materials reduced body reflected radiation and lessened measurement errors over the operational bandwidth of the monitor.
Although layering lossy materials has been tried what is desired is a body worn microwave radiation monitor having a frequency response that is immune to body reflected interference.